This PDF file contains the front matter associated with SPIE Proceedings Volume 11838 including the Title Page, Copyright information, and Table of Contents.

This presentation summarizes advancement in 3-dimensional position-sensitive room-temperature semiconductor gamma-ray spectrometers and imagers. Applications of 3-D CZT detectors in national security, nuclear power industry, international nuclear safeguard, space exploration and medical imaging, will be introduced. Sustained advancement on CZT detector technology, including larger detection volume, next-generation digital application specific integrated circuit (H3DD-UM ASIC) and integrated electronic data acquisition systems will be described, as well as research and development on alternative semiconductor gamma-ray spectrometers.

We report on the results from testing CdZnTe (CZT) position-sensitive virtual Frisch-grid (VFG) detectors and a prototype of a 16x16 detector array proposed for a high-energy gamma ray imaging space telescope. Previously, we evaluated the spectroscopic performance of these detectors. Here, we present results from our detector performance studies with an emphasis on position resolution. We employed digital waveform capturing and analog ASIC based approaches to read out the signals from the detectors and evaluate their spectral- and spatial-resolution. The VFG arrays allow for the flexibility to scale-up the dimensions of the detectors for the desired efficiency, while the position information allows for correcting the detectors’ response non-uniformities caused by crystal defects and device geometry, thereby reducing the instrument cost and making them more feasible for emerging applications in gamma-ray astronomy, nonproliferation, portal screening and nuclear safeguards, where large

Radiation detectors, especially for X- and gamma-rays, are being developed rapidly that utilize the advantages of semiconductor detectors operating at room temperature. CdTe and CdZnTe based detectors have successfully dominated the commercial market. Both the materials, however, face limitations due to the presence of high concentrations of intrinsic defects such as Te inclusions and sub-grain boundaries. In the recent years, we have observed that the addition of selenium circumvents many issues pertaining to CdTe/CdZnTe. As a result, the new quaternary material Cd1−xZnxTe1−ySey (CZTS) is emerging as a next-generation room temperature radiation detector material with the potential to supersede CdZnTe, competing in both cost and detector performance. In this presentation we will discuss the path toward optimization of the composition of the quaternary compound for the best detector performance.

We have assessed the efficacy and application of a commercially manufactured cadmium zinc telluride (CZT) gamma imaging camera. The imaging system manufactured by H3D Corporation (Ann Arbor, Michigan) is intended for practical field applications by first responders and nuclear power plant surveyors. The H3D imager (Model H420) uses a position-sensitive, pixelated CZT element <19 cm³ in volume with gamma energy resolution of <1.1% FWHM at a reference gamma energy of Cs-137 (662 keV) to develop fast (less than 2 minutes start-up time), lightweight (8.6 lb) gamma imaging systems. The Model H420 gamma imager’s automated mask/anti-mask uses a rank-19 coded aperture mask for improved signal-to-noise ratio and cleaner images; it also benefits from the Compton imaging technique. Options for better quality CZT crystals with ≤0.8% FWHM resolution at 662 keV are available. The system’s integrated range finder can precisely overlay gamma ray and optical images from point-like or extended gamma emitting sources alike, which can show the extent of a radiological spill. The CZT imager enhances the surveillance capability of the first responders in targeted search and radiological emergency response. Comparative in-depth references will be made to the progress made since the original concept of applying 3D, position-sensitive, pixelated CZT in the area of materials development (crystal growth techniques), detector mounting, electronic readout of the application-specific integrated circuits (ASICS), event reconstruction algorithm, calibration procedures, and noise reduction techniques to imaging.

We report the implementation of a deep convolutional neural network to train a high-resolution room-temperature CdZnTeSe based gamma ray spectrometer for accurate and precise determination of gamma ray energies for radioisotope identification. The prototype learned spectrometer consists of a NI PCI 5122 fast digitizer connected to a pre-amplifier to recognize spectral features in a sequence of data. We used simulated preamplifier pulses that resemble actual data for various gamma photon energies to train a CNN on the equivalent of 90 seconds worth of data and validated it on 10 seconds worth of simulated data.

A new line of G4S detectors has been developed at Crytur, which combines the high-Z scintillators GAGG:Ce and LuAG:Ce with Silicon photomultipliers (SiPM). The detectors’ performance was established by identifying natural radionuclides in samples of rock and building materials. Due to the high detection efficiency of the chosen scintillator materials, and the small footprint of SiPMs, these detectors are very compact and can be made rugged for applications of gamma-ray detection and spectroscopy in the range of 30 keV to several MeV. Crytur’s material development and coupling design make these detectors a superior and affordable alternative to the conventional NaI:Tl based detectors. Due to the compact size these detectors are portable and suited for both lab and field use

Plastic-based scintillator detectors have many advantages over inorganic scintillators, including mechanical ruggedness and cost. However, their range of application has generally been limited by their lack of gamma spectroscopic performance. We have been developing metal-organic doped plastic scintillators which allow for spectroscopy while maintaining the advantages of plastics. These scintillators allow for the use of plastics in many new application spaces. Using iridium based fluors, bismuth loaded plastics have demonstrated high light yields of >20,000 photons/MeV and good energy resolution (<12% FWHM at 662keV) in modest sizes. We are working on scaling up these scintillators to larger sizes for use in radio-isotope identification (RIID) type application. This work was supported by the US DOE Office of NNSA NA-22 DNN Program and was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

We report on a small gamma spectrometer with directional detection, based on two modules. Each module contains an array of 128 scintillator pixels coupled to reverse-biased photodiodes, an ASIC and a microcontroller. Modules communicate via USB and are operated via an Android GUI on a WiFi-connected device. Transparent ceramic GYGAG ((Gd,Y,Ce)3(Ga,Al)5O12) garnet scintillator pixels offer energy resolution as good as 3.1% at 662 keV for individual pixels. We previously reported on an eight-module planar spectrometer, based on the same technology1. The current compact system uses two modules in a back-to-back configuration to improve its speed and accuracy in locating a gamma-emitting source in a 4-pi field of view. This dual module system (~2.5 x 2.5 x 3.5 inches) is suitable as a pager-sized RIID or spectroscopic personal radiation detector (SPRD). Multiple dual module units can be combined for improved efficiency. Spectroscopic and directional performance will be described.

Plastic scintillators utilizing iridium complex fluorophores offer substantial improvements in light yield, and their light yield is not significantly quenched in compositions with bismuth metalorganic loading, at a loading level of 21 wt% bismuth metal. This new bismuth plastic (Ir-Bi-Plastic) offers improved detection efficiency over commercial plastic scintillators. One application for Ir-Bi-Plastic is in low-cost, portable, and durable dual-particle imaging (DPI) systems supporting nuclear safety, security, and safeguards. However, new materials must undergo investigation using industry standards to quantify their capabilities. In this work, an Ir-Bi-Plastic was experimentally evaluated as a small, pixelated radiographic array in a fast neutron environment, with individual pixel dimensions of 2×2×19 mm. For comparison, identical evaluations were conducted for two similarly sized arrays made from EJ-200 and EJ-256. A separate Ir-Bi-Plastic array with 5×5×20 mm pixels was also evaluated. ASTM methods were leveraged to determine the modulation transfer function and spatial resolution for each array. Edge response measurements of a 2-in thick tungsten block were recorded by pressure coupling all four arrays to a commercial a-Si digital radiographic panel. Experimental results were then compared for all four arrays, and the results demonstrated that the Ir-Bi-Plastic outperforms similar arrays made from EJ-200 and EJ-256 (5 wt% Pb). These findings suggest that DPI systems utilizing Ir-Bi-Plastic hold promise for continued development over older, more traditional, alternatives.

Perovskites are a family of semiconductor materials with molecular formula ABX₃ [where A⁺ = Cesium (Cs), methylammonium (MA or CH₃NH₃) or formamidinium (FA or CH(NH₂)2), B-site is metal, and X− = chlorine (Cl), bromine (Br) or iodine (I)] that have recently seen a surged interest for X-ray and gamma-ray detection. The all inorganic version, CsPbBr₃, grown by high temperature melt method has been demonstrated with an impressive gamma-ray energy resolution of 1.4%@662 keV, while the solution grown CsPbBr₃ showed the best achievable resolution of 5.5% at the same energy from a 137Cs source. This paper gives an overview of the development of perovskite in both X-ray detection and gamma spectroscopy, including the most recent advancement with perovskite single crystal grown by low temperature inverse temperature method for solid-state X-ray detector. The crystal shows a decent long carrier diffusion length that is ideal for charge collection, while their mobilities are still not on par with CdZnTe. We also reported our most recent development on clarifying the concepts around X-ray detection limits. The X-ray sensitivity and the lowest detectable dose rate (i.e., X-ray detection limits) of several MAPbI3 detectors made of single crystal were experimentally measured. The best achieved X-ray sensitivity is ~2.5E4 μC/Gy_air/cm² under 15.4 V/mm, which is comparable to the current state-of-the-art MAPbI₃ based X-ray detectors (~ 2.3E4 μC/Gy_air/cm² under 4.2 V/mm for GAMAPbI₃ (GA=guanidinium) single crystal detector). The best achieved lowest detectable X-ray dose rate for the same MAPbI₃ detector is ~61 nGy_air/s under 15.4 V/mm, and decreased to ~24 nGy_air/s under 3.8 V/mm. The good performance of the MAPbI3 detectors further proves their great potential as the next generation low-cost X-ray detector.

X-ray scintillators are scintillation-based detectors, which absorb and down convert high-energy ionizing radiation into ultraviolet-visible light for detection of X-rays. They are actively used in many areas, including medical imaging, non-invasive inspection, radiation monitoring, and so on. Most of commercially available X-ray scintillators are based on inorganic single crystals, which are prepared via energy-consuming high temperature processes. To reduce energy consumption for material preparation, many organic scintillators have been developed via low temperature processes, which however have inferior performance than inorganic ones with low scintillation light yields and resolutions. Another issue of inorganic single crystal X-ray scintillators is the lack of flexibility, which could limit their applications in many areas where curved surfaces are present. It is there of great interest to develop new generation high performance X-ray scintillators that could be facilely prepared, flexible, and eco-friendly. In this talk, I will present our recent efforts on the development and study of highly efficient eco-friendly X-ray scintillation materials based on organic metal halide hybrids, which exhibit many advantages over conventional X-ray scintillation materials, e.g. (i) facile preparation via wet chemistry at room temperature using low cost rare-earth free raw materials, (ii) tunable visible emissions with near-unity photoluminescence quantum efficiencies, and (iii) higher light yields than most of conventional commercially available scintillators. X-ray imaging tests have shown that these new scintillators provide an excellent visualization tool for X-ray radiography, and high resolution flexible scintillators can be fabricated by blending these materials with appropriate polymers.

This presentation will demonstrate a new class of versatile X-ray detectors based on organometallic perovskite semiconductors. Organometallic perovskite semiconductors have emerged as a new generation of photovoltaic material. It is also an excellent candidate for room temperature radiation detection due to the presence of high-Z elements such as Pb. Although there have been many studies with this class of materials for various applications, practical applicability and significant challenges, such as high dark current and low stability, that are specific to X-ray imaging still remain. This study has implemented various sensor compositions and configurations to develop X-ray detectors with low dark current and high X-ray sensitivity.

Despite years of impressive progress in development of new scintillators for gamma spectroscopy, energy resolution offered is still lagging direct detection solid state devices. Even the best scintillators do not convert more than about 30% of the initial energy into photons, and this introduces the Poisson component in the photodetector, which can become a limiting factor. On top of that, the efficiency of scintillation is strongly dependent on excitation density, so not only the number of generated photons is smaller than the initial number of electron-hole pairs, but the conversion process is subjected to additional fluctuations due to ionization density fluctuation (nonproportionality on average and pulse-to-pulse fluctuations). This stochastic pulse-to-pulse variation contributes to resolution limitation. Further progress in improving energy resolution requires to address all these issues at the same time: starting from high electron-hole production efficiency, through energy conversion into light, and ending on matching scintillation emission with superior sensitivity and noise characteristic of a photodetector. One route points to small bandgap materials (such as “black scintillators”) which have potential for obtaining extremely high light yields and match well high quantum efficiency of silicon-based photodetectors. In recent works we showed that europium-doped scintillators can be converted into near infrared emitters by samarium co-doping and provide high energy resolution in gamma spectroscopy. Alternatively, novel metal halide perovskites may become the way to higher energy resolution goal, but there are some significant problems to be solved. The ideas developed with “black scintillators” may alleviate some of obstacles found in perovskites.

Future HEP experiments at the energy and intensity frontiers present stringent challenges to inorganic scintillators in radiation tolerance, ultrafast time response and cost. This paper reports recent progress in radiation hard, ultrafast, and cost-effective inorganic scintillators for future HEP experiments. Examples are LYSO crystals for a precision time of flight detector, LuAG ceramics for a longitudinally segmented shashlik sampling calorimeter, BaF2:Y crystals for an ultrafast calorimeter, and cost-effective scintillators for a homogeneous hadron calorimeter. Applications for Gigahertz hard X-ray imaging will also be discussed.

Material identification is challenging for X-ray Computed Tomography (CT) when objects of interest composed of low atomic number (Z) elements are shielded by dense materials. Fast neutron CT (FNCT) can compensate for this shortcoming by providing both penetration through high-Z materials and good contrast in low-Z materials. Here we investigate improvements in X-ray CT feature identification using information from fast neutron imaging. To demonstrate the complementarity of X-ray and FNCT, simulated CT data sets were generated for two heterogenous, nested, cylindrical phantoms using the Monte Carlo N-particle (MCNP) transport code for both imaging modalities. Xray radiographs were simulated for polychromatic 300 keV and 9 MeV e-Bremsstrahlung X-ray sources, while a generic Gaussian D-T source spectrum [E_n(pk) = 14.10 MeV, w/ FWHM ~ 0.75 MeV] was used for the neutron radiographs. A total of 360 projections taken at 1° intervals were simulated for both modalities and phantoms. All projection data were reconstructed with filtered-back projection (FBP) using the Livermore Tomography Tools (LTT) code. Our results indicate improved material discrimination and resolution of certain features with combined X-ray and neutron CT data sets.

Fast neutron Computed Tomography (nCT) is a powerful and non-invasive imaging modality that can be used to examine features and defects within low Z elements (such as plastic) hidden or shielded by high Z elements (such as tungsten, lead, or even stainless steel). This study built a fast neutron radiography and nCT system and explored various multi-material complex objects utilizing a fast neutron beam at The Ohio State University Research Reactor (OSURR), which provides ~5.4 x 10^7 n·cm-2·s-1 neutron flux at 1.6 MeV (median energy). The lens-based system includes an Electron Multiplying (EM) CCD camera, a light-tight enclosure, and a high light yield 1 cm thick Polyvinyl Toluene (PVT) scintillator provided by Lawrence Livermore National Laboratory (LLNL). A variety of test exemplars were scanned, with the number of projections for each scan ranging from 90 to 180, covering either 180 or 360 degrees. The exposure time for each projection ranged down to one minute, enabling a full nCT scan within a few hours of operation at a 500-kW low power research reactor. 3D tomograms were constructed using Octopus reconstruction software. Results showed that not only could nCT projection data be successfully constructed into volume data, but good contrast between HDPE and a millimeter-sized tungsten ball could be obtained. The 3D tomography presents high contrast to clearly discern HDPE features and voids inside tungsten shielding that are not discernable using 2D radiography.

Fast neutrons accessible from 14-MeV D-T neutron generators have higher transmission through high-Z materials compared to radiography X-rays due to a more uniform attenuation as a function of material Z. These neutrons can therefore image low-Z materials even when shielded by high-Z materials. The constraints in portable fast-neutron digital imaging systems include limited neutron output, limited light produced by neutron imaging scintillators, and lower resolution images due to large source spot size and required scintillator thickness. In addition, digital panel dark-noise counts can be 100x higher than the image signal, and variations across the panel can also be comparable to this signal. We will discuss recent efforts to develop a portable neutron-radiography system, including improved neutron scintillator, mitigation of digital panel noise, and new portable D-T neutron generators. We will also present MCNP efforts to model the system, including neutron scattering effects.

A new large-area pixel detector for X-ray diffraction combining indirect conversion with charge integration and photon counting is described. Indirect conversion achieves a large active area with no gaps or dead areas and also a high Detective Quantum Efficiency across the energy range of interest for X-ray diffraction, from 6 keV to 24 keV. The detector runs in charge integration mode which allows photon counting with no counts lost to charge sharing or coincident pulse effects. The detector is also able to discriminate against high energy events from the natural background radiation which allows the acquisition of very long exposures with essentially zero noise.

Automation and remote control are added to a fast neutron tomography system at the Ohio State University Research Reactor (OSURR). The automated system with XYZ stages allows for an improved imaging efficiency and quality of computed tomography, while reducing total image acquisition time and keeping the user further from the neutron beam facility. The automation code was written in Python scripting utilizing the Tkinter GUI structure and modules for instrumentation control. A Python wrapper for Micro-Manager, pycromanager, is used to control the Electron Multiply (EM) CCD and CMOS cameras. The system has a three directional XYZ stage for precise alignment and a rotational stage to obtain the radiograph views for computed tomography. Both of these stages hold the imaging object and are external to the light tight box. Finally, another one direction stage is employed within the light tight box to move the camera for real-time focusing. Each stage is controlled through user defined functions that pull from the serial control offered by pyserial. Within the light tight box is the camera, a telecentric lens, a mirror, and a Polyvinyl Toluene (PVT) scintillator. The GUI allows for the users to input all of the experiment parameters such as exposure time, EM Gain (for EMCCD), file save information, and rotational requirements. Upon submission, the rotational degree information is passed into an algorithm to generate a list for a few view tomography. As the imaging system takes and saves the images, the users are shown the progress in real time through messages and pictures in the GUI.

Lens-coupled X-ray computed tomography (X-ray CT) using a transparent scintillator imaged on a CCD camera obtains higher spatial resolution than the more commonly employed phosphor-enhanced amorphous silicon (A-Si) panels. A-Si panels are limited to resolution typically greater than ~200 microns, have a limited working life due to degradation with dose, and provide intrinsically low efficiency with thin (few hundred microns thick) phosphor coatings. Demanding applications such as imaging the interior of complex additively manufactured components require high throughput and high resolution, best achieved with a lens-coupled system. However, for large fields-of-view, very large area but thin transparent scintillators are required – a format difficult to fabricate with high light yield single crystals – therefore, glass scintillators with both modest X-ray interaction and light yield have been used for years. We have developed a new polycrystalline transparent ceramic scintillator, Gd0.3Lu1.6Eu0.1O3, or “GLO,” that offers excellent stopping power and light yield for improved contrast in sizes up to 14” x 14” plates, with thicknesses in the 2-10 mm range, and we are implementing it in systems to increase imaging throughput for 9 MeV Bremsstrahlung X-ray CT. CT imaging performance will be described.

Compliance of member States to the Treaty on the Non-Proliferation of Nuclear Weapons is monitored through nuclear safeguards. Recent developments in scintillation detectors and electronics have enabled important improvements in safeguards systems. In this talk, I will present recent results in the characterization of a new deuterated stilbene scintillator and associated algorithms for neutron spectrum unfolding. I will then give an overview of how similar algorithms can be applied to identify and hence track TRISO fuel pebbles in high temperature gas or molten salt-cooled reactors.

Nicholas Myllenbeck is a Senior Member of the Technical Staff at Sandia National Laboratories in Livermore, CA. His research interests are in organic scintillator development and characterization, biomaterial and plastic valorization using synthetic chemistry, and environmental aging of organic materials. Nicholas has developed environmentally aging-resistant plastic scintillators, pulse-shape discriminating organic glass-polymer blends, and advanced processing methods for organic scintillators. He has twelve years of experience in small-molecule and polymer synthesis, including six years of organic scintillator research.

Scintillation materials for the spectroscopic detection of gamma photons have been made of inorganic crystals, organic liquid and plastic scintillators. These scintillators are either expensive for large-area detection or incapable of gamma spectroscopy. We have reported the syntheses of transparent liquids and plastic nanocomposites comprising high loading of high-Z nanoparticles for gamma photoelectric generation and conjugated organic luminescent systems for visible photon generation. Hafnium oxide nanoparticles and cadmium zinc sulfide quantum dots were loaded into the organics up to 60 wt% via methacrylate-terminated surface functionalization. The liquid scintillator loaded with 40 wt% hafnium oxide nanoparticles demonstrated a light yield of 11699 photons/MeV with an energy resolution of 14.8% for 662 keV gamma. The 60 wt% CZS QD loaded plastic nanocomposite exhibited an optimized light yield of 9275 photons/MeV and produced a gamma photopeak. A radiation hardness study indicates that the loaded liquids and nanocomposites exhibits comparable hardness to the unloaded scintillators.

The three most popular radiation oncology technologies are based on using beams of photons, electrons, and hadrons (protons and heavy ions). Photon radiotherapy is currently a quite mature and advanced technology. However, it continues to evolve toward improvement of its medical effectiveness and set new requirements for the radiation source, which is typically an electron linear accelerator (linac). For example, novel techniques that involve tumor irradiation from 4π angle or FLASH ultrafast delivery of large doses cannot be efficiently realized with the existing accelerators. At the same time, hadron radiotherapy promises improved treatment outcomes in certain cases. Efforts are underway to develop more compact hadron linac technologies with the ability to change the beam energy in millisecond time scales for efficient spot scanning. In this paper we will overview the current trends in linac technologies for electron, photon and hadron therapy, and provide examples of such developments at RadiaBeam.

We present an analytic method for the calibration of X-ray fluorescence spectra collected using cylindrically bent crystal analyzers in any arrangement with respect to the sample and detector. Cylindrically bent analyzers are often used in the von Hamos geometry at X-ray Free Electron Lasers to image and disperse fluorescence from a point source to an easily calibrated line. When not in the von Hamos configuration, cylindrically bent analyzers produce spatio-spectral patterns that cannot be calibrated using existing methods. Our formula allows us to rapidly fit and optimize geometric parameters for fluorescence data and calibrate the resulting spectra.

As part of an on-going program of X-ray polarimeter development at NASA Goddard Space Flight Center, we have built a Hard X-ray Photoelectric Polarimeter (HXPP) designed for astrophysical observations in 10-60 keV band. HXPP’s detection method is based on photoelectric effect and a gas micro-pattern time projection chamber technique. This allows us to tune polarimeter sensitivity to the bandpass of interest by selection of gas type and gas pressure. Here we report on the first experimental results for measuring X-ray signal above 20 keV with HXPP filled with a mixture of 80% argon and 20% dimethyl ether at the total pressure of 2.5 atm.

NIST has developed microwave multiplexed microcalorimeter arrays for the detection of hard X-rays andγ-rays (Bennett et al. 2012, Mates et al. 2017). The arrays are made of tin or bismuth absorbers that are read-out with arrays of Transition Edge Sensors (TES). Each TES is coupled via a SQUID to a microwave resonator, and a single microwave line is used to sample the response of the resonators of all pixels. The detector arrays achieve an energy resolution of 55 eV FWHM at 97 keV. We report here on the performance of a 34-pixels prototype TES with a collimated 50μm diameter 20-50 keV X-ray beam as well as a Eu(152) source for a future balloon flight. We will furthermore describe a planned stratospheric balloon flight that will be used to demonstrate the performance of a novel mini-dilution refrigerator and the 34-pixels prototype detector in a space environment.

This work investigates the capabilities of a state-of-the-art photon counting CdZnTe Timepix3 detector by combining sub-pixel resolution and energy weighted imaging to resolve and identify metallic particles (< 35 µm) in contaminated pharmaceutical hard capsules. While previous pixelated photon counting semiconductor detectors such as the Timepix or Medipix3 allowed single event analysis only for low photon fluxes that are rather unsuitable for imaging purposes, the new Timepix3 detector allows for the analysis of single events even at high X-ray fluxes due to its data driven data output. The challenges of the project like sufficient charge collection and processing of larger data sets for sub-pixel imaging, the influence of charge sharing and X-ray fluorescence on the spatial and energy resolution as well as 3 different approaches of the energy weighted identification of the metallic powders will be discussed.

CsPbBr3 and other perovskite semiconductors are rapidly emerging as strong competitors to TlBr and CZT, both in terms of innate properties and potentially significantly lower production cost. These crystals can be grown from the solution as well as melt. However, there has been very few studies on understanding the effects of bandgap and crystalline defects, polarization, stoichiometry and other growth parameters on the charge transport properties and detector reproducibility. In this study, we will report on these interconnected parameters for CsPbBr3 gamma detectors grown by the Bridgman technique.

Ga₂O₃ has recently emerged as an attractive ultrawide bandgap material for a wide range of extreme-condition sensing applications. Besides its excellent performance as a semiconductor radiation detector material, Ga₂O₃ also exhibits great potential as a scintillator. Its scintillation performance can be tuned through appropriate growth control and well-designed doping. In this presentation, we will report on the temperature-dependent scintillation performance of Ga₂O₃ with a focus on its high scintillation yield and fast decay time. These characterization results will be correlated to Ga₂O₃’s intrinsic properties and material processing conditions.

Electron-based diagnostics at the National Ignition Facility use Sandia’s Icarus sensors for ultrafast imaging. However, the electron detection performance of these sensors has remained mostly unknown. Previous work characterized the singulated Common Anode photodiode structure of the ”Furi” and ”Hippogriff” but did not include the Common Cathode photodiode structure of the Icarus. Using a fully fabricated Icarus sensor, we measured the cross-sectional geometries and modeled the expected performance; then, we measured the sensor’s EQE, quantum yield, and charge gain with an electron gun. These measurements were essential to understanding the space-charge limitations of the electron-based diagnostics that use them.

Energy weighting is an efficient technique for improving image contrast. If finally evaluating through human visual information, it is fascinating how the contrast of the image changes due to the difference in the weighting of X-ray energy. Therefore, we tried to evaluate how X-ray energy and contrast affect each other by comparing with gamma correction, which is a contrast adjustment performed in general image processing. Since the interaction in X-ray imaging is complicated, We replaced the imaging system with a simple one, and the change in the image due to the difference between energy-integrated and photon-counting detectors is represented as a tone curve. Simulation is a suitable technique for calculating the change in pixel value due to the difference in the weight of X-ray energy. Still, it requires creating a model for each imaging target. Therefore, to estimate the change more easily, we examined how to simplify the imaging system.

An avalanche effect yielding inherent gain can be exploited in thin, single-crystal chemical vapor deposition (scCVD) diamond. It occurs when a high enough bias is applied across the diamond thickness while avoiding breakdown. This charge multiplication effect was studied previously with alpha particles and heavy ions either by using the transient current technique or by measuring the energy spectrum. The measurements we obtained to evaluate the charge multiplication performance of a 10 μm thick scCVD diamond detector used a novel approach—we employed an electrometer to characterize the response of the detector by performing directly coupled current measurements (time-averaged charge, at 1 Hz sampling) when exposed to 14.1 MeV neutrons from deuterium-tritium fusion. We measured both the dark and irradiated currents from the detector over a range of applied displacement field values from 2 to 75 V/μm. A histogram method with central mean and standard deviation width was used to determine the current over each measurement duration typically from 100 to 300 seconds. The dark-subtracted irradiated current (i.e., contrast) was used to evaluate the gain of the detector at each applied displacement field. The contrast at an applied displacement field between 15 and 20 V/μm was higher than the expected linear increase in contrast proportional to the increased applied bias, indicating the possible presence of avalanche events in the diamond. The detector response also indicated possible polarization and charge depletion effects. These results provide an opportunity to further explore the use of thin scCVD diamond as a fast neutron current mode detector with inherent gain.

Silicon carbide (SiC) is the only wide-bandgap semiconductor to possess native oxide layer thus favoring efficient fabrication of metal-oxide-semiconductor (MOS) devices. 4H-SiC MOS structure has recently been demonstrated as improved radiation detector compared to the conventional Schottky barrier architecture. We report the fabrication of vertical Au/SiO₂/n-4H-SiC MOS capacitors for radiation detection, by dry-oxidation of 20 μm thick n-type 4H-SiC epitaxial layer in air at 1000°C. Charge-carrier traps (defects) are known to limit the performance of semiconductor devices. In order to characterize the defects, capacitance mode deep level transient spectroscopy (C-DLTS) was carried out. Apart from regular electron-traps e.g., Ti-impurity and Z1/2 sites, we have also observed the carbon-interstitial related hole traps HK3. While studying defect centers in these devices using a filling pulse peaking to 0 V from a quiescent reverse gate voltage VG = -4 V, we observed a robust positive peak centered around 650 K. Positive peaks in C-DLTS scan indicates minority-carrier trapping, although above-mentioned type of filling pulses does not populate minority-carrier trap centers normally. The activation energy of the observed trap, most likely a carbon vacancy (HK₃), was calculated to be 1.27 eV above the valence band edge.

Thick 4H-SiC epitaxial layers are essential for high-resolution detection of x- and gamma-rays in harsh environment. In this work, we have fabricated high-resolution Ni/n-4H-SiC Schottky barrier radiation detectors on 250 μm epitaxial layers, the highest thickness ever reported. Capacitance-voltage (C-V) measurements showed a low-carrier concentration of ≈2 × 10¹⁴ cm^-3 which based on simulations of the electric field allow the detectors to be fully depleted without break down. Current-voltage (I-V) characteristics displayed low leakage currents of < 1 nA up to − 800 V. To predict how the leakage current will grow at the large biases needed to fully deplete the detectors (at ~ 10 kV), the barrier lowering was evaluated from the detectors’ ln J/E_m vs. E1/2_m plots. Several detectors displayed scaling factors ≈ 2 or greater suggesting that leakage current should remain low even at extreme bias. Pulse height spectrometry using 5486 keV alpha particles showed a resolution of < 0.5 % full width half maximum (FWHM). From the charge collection efficiency vs. applied bias characteristics, the minority carrier diffusion length was found to be >10 μm. Both the long minority carrier diffusion length and high resolution were correlated to the low concentration of lifetime killing defects Z_1/2 and EH_6/7 (both associated with different charge states of carbon vacancy) found in the detector’s DLTS spectra

The design and technology of photodiodes manufacturing with a potential barrier as Schottky contact based on a substrate of radiation-resistant n-Hg₃In₂Te₆ single crystal are presented. The photosensitivity of the photodetector covers the wavelength range λ≈0.6-1.6 μm at the maximum current monochromatic sensitivity S_λ≈1.15 A/wt for the λ_max≈1.55 μm. To study the effect of contact material on the effect of the absorbed dose of ionizing radiation, two types of photodetectors Ni/n-Hg₃In₂Te₆/In and Cr/n-Hg₃In₂Te₆/Cr were fabricated. A study of the effect of absorbed doses of ionizing radiation D_γ1≈10⁵ , D_γ2≈10⁶ і D_γ3≈10⁷ Gray on the main parameters of photodetectors: S_&lambda;, λ_max, dark currents at forward and reverse bias, open circuit voltage, short circuit current. Photodiodes, based on mercury-indium telluride (HgInTe), showed high resistance to ionizing radiation. The best resistance to ionizing radiation was shown by Cr/HgInTe/Cr photodiodes, which slightly changed their basic parameters at the absorbed dose of D_γ3≈10⁷ Gray. Ni/HgInTe/In photodetectors lost their function after exposure to an absorbed dose of D_γ3≈10⁷ Gray. In Ni/HgInTe/In photodetectors the absorbed dose of D_γ3≈10⁷ Gray practically destroyed the indium contact. 30-50 % of nickel front contact was also destroyed. For comparison, similar studies were performed with photodetectors based on cadmium telluride Cr/CdTe/In, prepared by the authors and silicon too. As silicon-based photodetectors the industrial photodiodes were used.

The temperature dependences of electrical characteristics of semi-insulating p-like CdTe(111) crystals, produced by Acrorad and Chernivtsi National University (ChNU), for which both ohmic and rectifying contacts were formed, have been studied. An ohmic contact was created by coating the CdTe(111)A face with an Au using chemical deposition. A rectifying contact was formed by vacuum thermal evaporation of Cr onto the CdTe(111)B face. Prior to contact deposition, both the CdTe surfaces were treated with Ar plasma at different regimes. Ohmic contacts were created both on the surfaces perpendicular and parallel to the <111< direction. Special attention was paid to weakening the effect of a metal-semiconductor intermediate layer. The dark I-V characteristics of the Au/CdTe/Au samples with two ohmic contacts revealed essential features of the electrical conductivity. The electron-hole statistic based on the electroneutrality equation (EE) and space charge limited currents (SCLC) showed that the discrepancy between the resistivity activation energy in electric fields of 0.81- 0.83 eV, where Ohm's law was fulfilled and in 0.55-0.6 eV, where SCLC was observed, was due to compensation process features but not tunneling processes through an insulating layer, which was supposedly forming when an ohmic contact was created. With increasing bias voltage, a weaker temperature dependence of the dark current was explained by difference in the compensation degree of the CdTe crystals. This parameter and deep level energy position, which was responsible for the dark conductivity, were estimated using the EE solutions and measurements of the temperature dependences of the resistance and SCLC

In this work the structural, optical and electrical properties of Cd_1-x-yMn_xZn_yTe single crystals (x=0.10, 0.20, y=0.15) grown by the vertical Bridgman method were investigated. Based on differential thermal analysis results, it was found that the crystallization rate increases as the crystallization temperature (Ts) decreases. It is determined that the volume fraction of solid phase in Cd_0.75Mn_0.10Zn_0.15Te and Cd0.65Mn0.20Zn0.15Te alloys decrease to a minimum in the temperature ranges 1366–1389 K and 1363-1388 K, respectively. The activation energies of melting and crystallization processes for these alloys under different conditions are established. The linear character of the dependence between the preexponential factor (lnφ_sol.phase,0 and lnV_{melt., sol. phase,0}) and the activation energy of these processes is determined, which is evidence of a compensation effect. The band-gap value was estimated to be ~ 1.73 eV for Cd_0.75Mn_0.10Zn_0.15Te and ~1.84 eV for Cd_0.65Mn_0.20Zn_0.15Te at 300 K. Typical transmission images showed the presence of small Te inclusions (5- 10 μm) in the crystals. The electrical resistivity, obtained from the I-V curves, was ~10⁴ Ω·cm for both crystals and decreased slightly toward the end of the ingots.

The design and technology of photodiodes manufacturing with a potential barrier as Schottky contact based on a substrate of radiation-resistant n-Hg₃In₂Te₆ single crystal are presented. The photosensitivity of the photodetector covers the wavelength range λ≈0.6-1.6 μm at the maximum current monochromatic sensitivity S_λ≈1.15 A/wt for the λ_max≈1.55 μm. To study the effect of contact material on the effect of the absorbed dose of ionizing radiation, two types of photodetectors Ni/n-Hg₃In₂Te₆/In and Cr/n-Hg₃In₂Te₆/Cr were fabricated. A study of the effect of absorbed doses of ionizing radiation D_γ1≈10⁵ , D_γ2≈10⁶ і D_γ3≈10⁷ Gray on the main parameters of photodetectors: S_λ, λ_max, dark currents at forward and reverse bias, open circuit voltage, short circuit current. Photodiodes, based on mercury-indium telluride (HgInTe), showed high resistance to ionizing radiation. The best resistance to ionizing radiation was shown by Cr/HgInTe/Cr photodiodes, which slightly changed their basic parameters at the absorbed dose of D_γ3≈10⁷ Gray. Ni/HgInTe/In photodetectors lost their function after exposure to an absorbed dose of D_γ3≈10⁷ Gray. In Ni/HgInTe/In photodetectors the absorbed dose of D_γ3≈10⁷ Gray practically destroyed the indium contact. 30-50 % of nickel front contact was also destroyed. For comparison, similar studies were performed with photodetectors based on cadmium telluride Cr/CdTe/In, prepared by the authors and silicon too. As silicon-based photodetectors the industrial photodiodes were used.

We have reported CdTe FPDs with high resolution imaging and energy distinguish for multi energy spectral CT X-ray imaging, and it can acquire high amount of information. This study developed a system that aggregates and 3DCT-Xray data with boundary extraction function for high speed data communication. In the medical and industrial field, it is necessary to narrow down the desired information and confirm it quickly for mobile devices. The developed system enables to divide high volume information imaging data into multiple low data 3D object data by surface rendering technique. The imaged data were rendered only by host PC and selectively transferred to client device such as smartphone so that user want to check.

This study demonstrates a result of polarization effect of an X-ray imager that uses TlBr detectors with silver small electrodes. Although TlBr detectors are suitable for X-ray imaging applications because of the associated large attenuation coefficients and direct conversion behavior, realizing a flat-panel detector with TlBr involves developing processes. The demonstrated imager is constructed utilizing a combination of existing technologies; it comprises a plate electrode containing thallium metal to suppress the polarization phenomenon, pixelated silver electrodes with 80 µm pitch, and a photon-counting-type readout integrated circuit that can work in the hole as well as electron collection modes. As a result, it was reconfirmed that the polarization phenomenon is a serious problem for small electrodes as well as for large electrodes. In addition, the polarization could have accelerated by high X-rays flux. This result can motivate the development of polarization-tolerant small electrodes for TlBr detectors.

Radiation detectors in planar configuration has been fabricated using CVD grown single crystalline diamond detectors. The detectors exhibited high energy-resolution for both electrons and holes transport. The performance of the diamond detectors was found to be asymmetric with respect to the bias polarity. The optimized charge collection efficiency values and the electronic noise analysis suggested the performance of the detectors is limited by the presence of electrically active defects such as nitrogen impurity. Density functional theory-based defect calculations has been performed to determine the location within the bandgap of the plausible defects that might interfere with the charge transport.